Now that one mentions that person, he or she turns up. This old proverbial saying is, as John Ciardi pointed out, a leftover from the ancient superstitious belief that pronouncing the devil’s name will cause him to appear. Indeed, the full saying is, Speak of the devil and he’s sure to appear. For primitive peoples, one’s name was an essential part of one’s being, and to speak a name gave one some power over the person named. The roots of the cliché have been largely forgotten, and today it is most often voiced simply when a person one has been talking about unexpectedly appears on the scene.